1. Field of the Invention
The present invention relates to an image processing apparatus and a method of the same, and more specifically to an image processing technique for processing a plurality of input image data. The structure of the invention is applicable to a variety of devices and units for simultaneously processing a plurality of image data, such as video game machines.
2. Description of the Related Art
In image processing apparatus such as video game machines, a plurality of image data are often superposed one upon another and displayed as one overlapped image on a screen. Such processing is generally realized by previously determining a priority sequence of the plurality of image data and specifying a certain transparent area in the image data. The priority sequence of image data represents relative positions of image data on a screen or another display device. A conventional superposing process is described based on an example where a plurality of image data represent an image including an inside of a train and scenery seen through a train window. As shown in FIG. 10, a set of image data F shows objects such as a window frame seen in the train while another set of image data B represents scenery seen through the window.
The image data F representing inside of the train is located before the image data B representing the scenery on a display screen. A certain portion of the image data F corresponding to a window pane is specified as transparent. In superposing process of the two image data F and B, the image data F having a higher priority is selected except for the certain portion corresponding to the window pane while the image data B representing the scenery is selected for the certain portion. This generates an image where the scenery is seen through the train window.
FIG. 11 shows a conventional image processing apparatus for implementing such a process described above. The conventional image processing apparatus includes first and second external units 250 and 260 for generating image data. The first external unit 250 sends image data 290 pixel by pixel, priority sequence information 300 showing a relative position of the image data 290 with respect to image data 320 of the second external unit 260, and first attribute information 310 showing whether each pixel is transparent or opaque. The second external unit 260 transfers the image data 320 pixel by pixel and second attribute information 330 showing whether each pixel is transparent or non-transparent.
The priority sequence information and the first and second attribute information are input into a display image data determining circuit 280 for determining which image data is to be selected for each pixel. A selector 270 then switches image data based on results of determination and outputs the image data to form a real-time video image.
The conventional image processing apparatus is generally used for superposing only two image data, and is not applicable to superposing of three or more image data without a supplementary structure. A plurality of complicated, high-speed processing units are thus required for processing three or more image data. This makes the image processing apparatus undesirably expensive, bulky, and complicated. Change of the priority sequence of image data requires switching all of the signals from the plurality of processing units.
The conventional image processing apparatus can not execute multiple semi-transparent superposing, for example, composing an image where a certain object is seen through a transparent water tank. Namely, the conventional system can not execute sophisticated image processing like multi-stage data mixing of a number of input image data as often required in video games.
A known image processing apparatus, for example, as disclosed in JAPANESE PATENT LAYING-OPEN GAZETTE No. 62-264096, processes only one type of image data, and is not applicable to image data of different types, especially superposing of different types of image data.